In any electropolishing system, the basic requirement is to immerse the metal workpiece in an electrolyte and create an electric field between the workpiece and an electrode within that same electrolyte. Surface metal goes into solution and the electrical potential accentuates this metal removal at the micro-peaks where ions have easier access, with less reaction taking place in the micro-valleys where reactions are more difficult. Amperage, voltage and electrolytic concentrations are all adjusted to maximize this differential attack. The result is a chemical removal over the entire surface, but more accentuated in the ridges than in the valleys and resulting in a substantially smoother surface, and eliminating the micro-tearing and grooving which results from mechanical polishing techniques. Micrographic examination of mechanically polished surfaces show some tearing even at very low RMS values whereas electropolished metal surfaces show a complete absence of such features. It is of course, necessary to clean the workpieces thoroughly before immersion in the electrolyte, and then to remove all traces of electrolyte afterwards. A multi-tank system is used in conventional electropolishing. Workpieces or metal parts are first cleaned in one tank, immersed in a second tank to rinse, and then usually moved to a third tank for final rinsing. They are then placed in the electrolyte for polishing. After electropolishing, the workpieces go through as many as three rinse tanks to assure complete removal of all traces of electrolytes.
Electrolytes used in conventional stainless steel electropolishing systems are typically sulfuric and chromic acids, and open tanks must be carefully vented. Any discharge of such electrolytes must be treated prior to disposal of liquids into a sanitary system. Proper venting, proper treatment of liquid discharge, protective equipment for workers, and the isolation of facilities have made electropolishing relatively safe for stainless steels.
For titanium dental and orthopaedic implants and other components made from reactive metals, there are several serious shortcomings to existing systems since medical implant components are relatively small with low production rates and since the electrolytes required for titanium are hydrofluoric, acetic or perchloric acid based. These acids represent serious additional hazards for open tank systems. Multi-tank systems are seldom smaller than a 50 gallon size for each individual tank. This represents a sizable investment in the electrolyte, a sizable quantity involved from an environmental standpoint, and a sizable surface area from which fuming can occur.
It is technically feasible to build a smaller version of a conventional multi-tank system for titanium implants by incorporating the necessary environmental and personal safeguards. However, such a system would be costly and could not be operated in a shop or lab environment without extensive ventilation and utility modifications. An entirely new approach has been designed in the present system and several new capabilities have also been incorporated which are not available in conventional systems heretofore.